Corrosion-resisting Fe-Ni-Cr alloy

Abstract

Disclosed in an improvement in a known Ni-Cr-Fe alloy. The alloy of the invention contains 30 to 32% nickel; 26 to 28% chromium; 0.5 to 1.5% copper; 6 to 7% molybdenum; up to 2% manganese; up to 1.0% silicon; up to 0.2% aluminum; up to 0.03% carbon; 0.10 to 0.25% nitrogen; balance iron and usual impurities. The alloy of the invention has increased pitting corrosion potential and critical crevice corrosion and pitting corrosion temperatures whereas the resistance of the alloy to commercially pure phosphoric acid has not been decreased.

We claim: 
     
       1. An alloy consisting essentially of: 30 to 32% nickel; 26 to 28% chromium; 0.5 to 1.5% copper; 6 to 7% molybdenum; up to 2% manganese; up to 1.0% silicon, up to 0.2% aluminum, up to 0.03% carbon; 0.10 to 0.25% nitrogen; balance iron . 
     
     
       2. The alloy of claim 1 containing 0.14 to 0.22% nitrogen. 
     
     
       3. The alloy of claim 1 containing 0.16 to 0.20% nitrogen. 
     
     
       4. The alloy of claim 1 containing about 0.18% nitrogen. 
     
     
       5. A component comprising the alloy of claim 1. 
     
     
       6. The component of claim 5 having a rate of material removal below 0.5 mm per year in a solution heattreated state. 
     
     
       7. A structural part formed of an alloy consisting essentially of 30 to 32% nickel; 26 to 28% chromium; 0.5 to 1.5% copper; 6 to 7% molybdenum; up to 2% manganese; up to 1.0% silicon, up to 0.2% aluminum, up to 0.03% carbon; 0.10 to 0.25% nitrogen; balance iron and usual impurities, the part having a high resistance to corrosion and having a rate of material removal below 0.20 mm per year at 100° C. in commercially pure phosphoric acid with a chloride ion concentration up to 1000 ppm. 
     
     
       8. The structural part of claim 7 having a high resistance to pitting corrosion in neutral or acid aqueous media which has a high chloride ion concentration. 
     
     
       9. The structural part of claim 7 having a high resistance to crevice corrosion in neutral or acid aqueous media which has a high chloride ion concentration. 
     
     
       10. The structural part of claim 7 having a pitting corrosion potential of at least 1000 mV H  at 75° C. and of at least 800 mV H  at 90° C. in neutral aqueous media having a chloride ion concentration of an order of 20,000 ppm. 
     
     
       11. The structural part of claim 7 having a critical pitting corrosion temperature of at least 80° C. and a critical crevice corrosion temperature of at least 50° C. in acid media with a chloride ion concentration of at least 50,000 ppm . 
     
     
       12. The structural part of claim 7 having a resistance to intergranular corrosion. 
     
     
       13. The structural part of claim 7 having the properties of resisting stress crack corrosion and pitting corrosion under the conditions of an accelerated acid gas test. 
     
     
       14. The structural part of claim 7 of an alloy containing 0.14 to 0.22% nitrogen. 
     
     
       15. The structural part of claim 7 of an alloy containing 0.16 to 0.20% nitrogen. 
     
     
       16. The structural part of claim 7 containing about 0.18% nitrogen.